Alkaline exchange membranes or anion exchange membranes (AEMs) allow for the transportation of anions (e.g., OH−, Cl−, Br−) from the cathode to the anode in an electrochemical reaction. AEMs are a critical component of AEM fuel cells, where hydrogen and oxygen are used to generate electricity, with water as a byproduct. AEMs are also used in water electrolysis, where water is split into hydrogen and oxygen using electricity. In both AEM fuel cells and water electrolysis, hydroxide ions (OH−) are transported through the AEM, along with water molecules. AEMs may also be used, for example, in batteries, sensors, and as actuators.
Known AEMs are generally unsuitable for use in AEM fuel cells or water electrolysis. Many commercially-available AEMs are based on polystyrene, which is generally considered a poor choice for AEM fuel cells or water electrolysis. Other AEM materials contain an arylene ether linkage (—O—) in the mid-chain and a benzyltrimethyl ammonium group in the side-chain. This combination, however, has been found to be chemically unstable and to degrade easily under highly alkaline conditions.